[tracing] Add --provider-buffer-size to trace program

Comments

[tracing] Add --provider-buffer-size to trace program
This lets one specify buffer sizes of individual providers.
With a lot more providers now (due to devhost tracing), it'll be
much more useful to be able to set buffer sizes of individual providers.
Note that specifying ktrace_provider's buffer size still doesn't
change the buffer size used by the kernel.
Tested: CQ
fx shell trace record --provider-buffer-size=minfs
fx shell trace record --provider-buffer-size=minfs:
fx shell trace record --provider-buffer-size=minfs:x
fx shell trace record --provider-buffer-size=minfs:0
fx shell trace record --provider-buffer-size=minfs:65
fx shell trace record --provider-buffer-size=ktrace_provider:64
fx shell trace record --provider-buffer-size=ktrace_provider:64 --provider-buffer-size=minfs:/data:64
Change-Id: I62504bd2afe0a8d7cf16865ad2a3453abdf66d87